COT Refraction and Retinoscopy 3 — Questions and Answers
Question 1: Which test is used during subjective refraction to balance accommodation between the two eyes after binocular balancing?
- Prism dissociation test (Correct answer)
- Cover-uncover test
- Hirschberg test
- Worth 4-dot test
Correct answer: Prism dissociation test
The prism dissociation test uses vertical prisms to dissociate the two eyes so that each eye's accommodation can be balanced independently.
Question 2: A Jackson cross cylinder (JCC) is used to refine which two components of a refraction?
- Cylinder power and cylinder axis (Correct answer)
- Sphere power and vertex distance
- Add power and prism
- Pupillary distance and base curve
Correct answer: Cylinder power and cylinder axis
The JCC is a ±0.25 or ±0.50 D cross cylinder used to refine both the axis and power of the correcting cylinder.
Question 3: During static retinoscopy, the examiner uses a streak retinoscope. Rotating the streak reveals the principal meridians of astigmatism when the streak is:
- Aligned parallel to the axis of the reflex to show the fastest or brightest reflex (Correct answer)
- Perpendicular to the axis of the reflex
- At 45° to the reflex
- Horizontal only
Correct answer: Aligned parallel to the axis of the reflex to show the fastest or brightest reflex
In streak retinoscopy, aligning the streak with a principal meridian shows the reflex in that meridian most clearly for neutralization.
Question 4: A patient's best-corrected visual acuity is 20/30 with −4.00 +2.00 ×090. If you add −0.50 D of sphere and acuity drops to 20/40, what does this indicate?
- The endpoint was correct; additional minus over-minuses the patient (Correct answer)
- Latent hyperopia is present
- The cylinder axis needs rotation
- Accommodative spasm is present
Correct answer: The endpoint was correct; additional minus over-minuses the patient
A drop in acuity with additional minus confirms the previous endpoint was correct and more minus causes over-correction.
Question 5: What is vertex distance and why is it clinically important?
- Distance from corneal apex to lens back surface; affects effective power for high corrections (Correct answer)
- Distance between pupils; used for PD measurement
- Thickness of the contact lens; affects oxygen permeability
- Distance from retina to nodal point; affects image magnification only
Correct answer: Distance from corneal apex to lens back surface; affects effective power for high corrections
Vertex distance is the distance from the corneal apex to the spectacle lens back surface and significantly affects the effective power for prescriptions above ±4.00 D.
Question 6: The duochrome (bichrome) test uses red and green targets to refine sphere. The endpoint is when:
- Letters on both red and green backgrounds appear equally clear (Correct answer)
- Letters on the red side appear clearer
- Letters on the green side appear clearer
- All letters on both sides blur equally
Correct answer: Letters on both red and green backgrounds appear equally clear
At the correct endpoint, chromatic aberration places the circle of least confusion on the retina so red and green appear equally sharp.
Question 7: Which type of astigmatism has both focal lines in front of the retina?
- Compound myopic astigmatism (Correct answer)
- Simple myopic astigmatism
- Compound hyperopic astigmatism
- Mixed astigmatism
Correct answer: Compound myopic astigmatism
Compound myopic astigmatism has both principal meridians myopic, placing both focal lines anterior to the retina.
COT Refraction and Retinoscopy 3
Which test is used during subjective refraction to balance accommodation between the two eyes after binocular balancing?